The present invention generally relates to intravascular devices for treating certain medical conditions and, more particularly, provides a method of forming intravascular devices and certain novel intravascular occlusion devices. The devices made in accordance with the invention are particularly well suited for delivery through a catheter or the like to a remote location in a patient""s vascular system or in analogous vessels within a patient""s body.
A wide variety of intravascular devices are used in various medical procedures. Certain intravascular devices, such as catheters and guidewires, are generally used simply to deliver fluids or other medical devices to specific locations within a patient""s body, such as a selective site within the vascular system. Other, frequently more complex, devices are used in treating specific conditions, such as devices used in removing vascular occlusions or for treating septal defects and the like.
One common ailment increasingly being treated by minimally invasive transcatheter techniques is an aneurysm. Generally, an aneurysm is defined by a dilation of an artery or other vessel. Although aneurysms are sometimes referred to as only arterial phenomenon, as used herein, an aneurysm can occur in other channels in a patient""s body, such as veins or the like. The most common type of aneurysm is probably an arteriosclerotic aneurysm. Such aneurysms typically occur in larger arteries in the elderly due to weakening of the vessel walls by advanced cases of atherosclerosis.
Aneurysms are typically classified as being either axial or lateral. Axial aneurysms tend to involve the entire circumference of the blood vessel, causing an otherwise generally cylindrical length of the vessel to balloon outward. A lateral aneurysm is a distension of only one side of the vessel, typically taking the form of a saclike recess communicating with the lumen of the vessel. Such aneurysms are also referred to as xe2x80x9csaccularxe2x80x9d or xe2x80x9csacculatedxe2x80x9d aneurysms.
Aneurysms can occur at a variety of locations in a patient""s vascular system. For example, an abdominal aortic aneurysm is a relatively common type of aneurysm which involves a distension of the aorta, e.g. in the vicinity of the iliac arteries and inferior mesenteric artery. Cardiac aneurysms, which are bulges in a weakened ventricular wall, typically arise as a result of a myocardial infarction. So-called xe2x80x9cberryxe2x80x9d aneurysms are small, saccular aneurysms of cerebral arteries, which frequently resemble a small berry.
In the past, aneurysms were frequently treated by direct surgical intervention. For example, to treat a lateral aneurysm in a vessel in the abdominal cavity, a surgeon can simply open the abdominal cavity and physically install a clamp around the base of the aneurysm to prevent, or at least limit, communication of blood between the aneurysm and the lumen of the vessel. This relieves pressure on the aneurysm, causing it to shrink. This could be very problematic for treating certain types of aneurysms, such as Cardiac aneurysms or cerebral berry aneurysms, due to the difficulty of safely accessing and surgically treating the aneurysm.
More recently, attempts have been made to develop minimally invasive techniques for treating aneurysms. Axial aneurysms in larger vessels are frequently treated by using stents and grafts. These devices basically reline the lumen of the vessel to provide some structural integrity and, in many cases, act as a prosthetic replacement for the affected length of the vessel. In some cases, the graft is relatively non-porous, enabling it to define a new lumen essentially as soon as it is in place in the vessel. More porous grafts and stents can also be employed as they can reduce pressure on the aneurysm and, long-term, provide a framework for endothelial ingrowth which allows the define a new, stronger vessel wall.
It is also possible to treat a lateral aneurysm with a graft or stent in much the same fashion that one treats an axial aneurysm. In such a circumstance, the graft occludes the neck of the aneurysm, or at least reduces blood flow into the aneurysm through the neck. Effectively stenting or occluding the neck helps reduce the size of the aneurysm and the likelihood that the aneurysm will rupture.
One disadvantage of using a graft in a circumstance such as this, though, is that the graft lines substantially more of the vessel than is necessary. This places a significant surface area of the graft into direct contact with stronger, healthier tissue of the vessel wall. Although the exact mechanisms are not well understood, it appears that this contact between a stent or graft and the vessel wall can cause neointimal hyperplasia and other ailments of the tissue of the vessel wall. Due to the potential for such collateral tissue damage, stents and grafts may be less desirable for use in treating lateral aneurysms than they are for axial aneurysms.
Current techniques for minimally invasive treatment of lateral aneurysms also include processes for filling the aneurysm. Such techniques usually involve either the placement of an expandable balloon in the aneurysm or filling the aneurysm with a thrombolytic agent or structure. For example, detachable occlusion balloons have been used for a number of medical procedures. These balloons are carried at the end of a catheter and, once inflated, can be detached from the catheter. Such a balloon may be positioned within an aneurysm, filled and then detached from the catheter. Deploring the balloon within the aneurysm can be rather difficult due to the high rates of blood flow through the aneurysm. Once in place, the operator typically fills these balloons with a fairly solid medium, such as biocompatible plastic beads, helically wound coils or the like. Once the balloon is filled to substantially fill the aneurysm, the balloon will substantially reduce the stresses on the vessel wall and reduce the tendency of the aneurysm to rupture.
The other technique for filling lateral aneurysms involves placing within the aneurysm structure which will tend to thrombose and fill the aneurysm over a relatively short period of time. For example, one can take a fairly long, helically wound coil and shove the coil so that it is packed within the aneurysm. Over time, a clot will tend to develop around the coil and effectively occlude the aneurysm. This process may be enhanced by increasing the surface area of the coils, such as by having strands of polyethylene extending outwardly from the surface of the coil. Such a product is commercially available from Target Therapeutics.
Such aneurysm filling techniques have their problems, as well. In deploying these devices, it is frequently difficult to keep them within the aneurysm. They be dislodged during the sometimes lengthy deployment process, but one can frequently retract or retrieve them rather than allowing them to float in the bloodstream and, potentially, embolize a vessel downstream. Even after they are deployed, though, they can still present some risks. When the balloon is filled, for example, an operator does not want to overfill the balloon due to the possible risk that the pressure of the balloon will rupture the aneurysm. Accordingly, the balloon may be slightly too small, potentially releasing the balloon from the aneurysm into the bloodstream. To avoid this risk, an operator may also deploy a stent or graft in the vessel to keep the articles filling the aneurysm in place, giving rise to the same problems noted above in connection with the discussion of such treatments.
The present invention provides a method for forming aneurysm occlusion devices from a resilient metal fabric and certain aneurysm occlusion devices which can be formed in accordance with this method. In the method of the invention, a metal fabric formed of a plurality of resilient strands is provided, with the wires being formed of a resilient material which can be heat treated to substantially set a desired shape. This fabric is then deformed to generally conform to a molding surface of a molding element and the fabric is heat treated in contact with the surface of the molding element at an elevated temperature. The time and temperature of the heat treatment is selected to substantially set the fabric in its deformed state. After the heat treatment, the fabric is removed from contact with the molding element and will substantially retain its shape in the deformed state. The fabric so treated defines an expanded state of a medical device which can be deployed through a catheter into a channel in a patient""s body.
In accordance with an alternative embodiment of a method of the invention, an aneurysm in a channel in a patient""s body may be identified and its general dimensions may be determined. A distal end of a catheter can be positioned adjacent the aneurysm; the distal end of the catheter may optimally be positioned within the aneurysm. An aneurysm occluder of the invention having appropriate dimensions for the aneurysm to be treated can be selected, whereupon it is collapsed and inserted into the lumen of the catheter. The occluder is urged through the catheter and out the distal end, whereupon it will tend to return to its expanded state. A body portion of the occluder is thereby positioned within the aneurysm itself. The rest of the occluder is deployed such that a central portion is positioned in or adjacent the neck of the aneurysm and an anchor is positioned within the lumen of the vessel.
Further embodiments of the present invention also provide specific aneurysm occlusion devices which may be made in accordance with the present invention. Such devices of the invention are formed of a metal fabric and have an expanded configuration and a collapsed configuration. The devices are collapsed for deployment through a catheter and, upon exiting the distal end of the catheter in a patient""s channel, will resiliently substantially return to their expanded configuration.
In accordance with a first of these embodiments, an aneurysm occlusion device has an anchor sized to be received within a lumen of a vessel. A differently sized, preferably larger, body portion is connected to the anchor by means of a central portion. The body portion and the anchor desirably are larger than the neck of the aneurysm which the device is to occlude; the central portion of the occluder is preferably no larger than, and ideally is smaller than, the neck of the aneurysm.